Is a guarantee valid if the guarantor says: 'I guarantee so-and-so if you bring him at such a time, otherwise I guarantee so-and-so,' or 'otherwise I guarantee the money owed by so-and-so'?
Chapter on Guarantee (Daman)
Al-Mughni
Book of Assignment (Transfer of Debt)
Primary text
This is invalid according to the Qadi because the first part is time-limited (Muwaqqat), and the second part is suspended upon a condition (Mu'allaq 'ala shart).
Supporting text
Abu al-Khattab states that both forms are valid.